More stringent emissions regulation on the amount of diesel particulate matter (DPM) and other gaseous constituents allowed in the exhaust gases of diesel engines has led to the use of exhaust aftertreatment devices such as diesel particulate filtration devices (DPF) and Diesel Oxidation Catalysts (DOC).
DPFs filter particulate matter from the exhaust gases to prevent it from exiting the tailpipe. After a period of operation, the collected particulate matter clogs the filter. The filter either needs to be replaced or removed for cleaning, which is not practical, or may be cleaned through a process known as regeneration. DPM is made up primarily of carbon, and is therefore combustible. Regeneration is a process where temperatures of the exhaust gases are made high enough to combust or oxidize the DPM within the filter. The regeneration process can cause the temperature of the exhaust gas exiting the diesel particulate filter to be well in excess of 600° C. By comparison, normal operating exhaust temperature for a diesel engine depends on the load and can range from about 100° C. at idle to about 500° C. at high load.
At highway speeds, high exhaust temperatures do not usually pose problems because the relatively high air speeds tend to disperse widely the heated gases. Exhausting the higher temperature gas stream can create difficulties when the vehicle is stationary or moving at low speed and is near combustible materials. For example, the stop and go movement of a trash collection truck on a street with overhanging trees could present difficulties. A truck typically has an exhaust stack pipe rising from the chassis adjacent to the truck cab. High temperature exhaust can produce a hot spot on the truck cab or trailer, or direct hot gases to a combustible substance, such as a building structure (for example, a loading dock or in a garage) or an overhanging tree.
It is desirable to provide an arrangement and a method for lowering the temperature of engine exhaust, particularly when the engine is operated for regeneration of exhaust aftertreatment devices.
In addition, in vocational trucks (dump trucks, trash hauling trucks, etc), the exhaust stack and the exhaust gases must not interfere with the operation of the body, lifting the dump body, for example.